Lower extremity peripheral arterial disease (PAD) affects 12% of men and women over age 65 and is associated with risk of cardiovascular death. PAD can be diagnosed and quantified in the ambulatory setting with the ankle brachial index (ABI). This study will define the prognostic significance of the ABI for functional outcomes and cardiovascular morbidity and will describe changes in functional status over time among PAD patients. Our results will help determine whether the ABI should be used for targeted screening.